Seat back



FIG. 1 is a front perspective view of a seat back showing my new design; the support post, the seat bottom and legs, which are shown in broken lines, form no part of the present invention;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is a top view thereof; and,

FIG. 7 is a bottom view thereof. 

The ornamental design for a seat back, as shown and described. 